Summary

We used flow cytometry to detect antiplatelet antibody-related microparticles (MP) in 56 patients with idiopathic thrombocytopenic purpura (ITP). We measured MP in platelets following various types of stimulation in two experimental systems. In one system washed platelets were incubated with normal serum which included the complement system, and in the other, washed platelets were incubated with Tyrode's buffer. There were no differences between the two measurement systems in the degree of increase in MP using various agonists. An increase in MP using ITP plasma was found in 12 out of 56 patients. In particular, four patients showed a significant increase in MP in washed platelets (WP) plus serum. Furthermore, the increase in platelet-associated IgM (PAIgM) was significant in these patients. There was also a definite positive correlation between PAIgM and the percentage of MP of WP plus serum. On the other hand, no specificity for MP formation with anti-GPIIb/IIIa or anti-GPIb autoantibodies was observed. IgM antibody-related MP appear to exist in some patients with ITP.